Mexico City air pollution spikes to 6 times acceptable limit

<p>MEXICO CITY &mdash; Small-particle pollution spiked in Mexico City to almost six times acceptable limits Sunday, a level not seen for years in the Mexican capital. </p>
<p>Levels of small particles, known as PM10, reached 581 points in the city’s Iztapalapa borough, on a scale where 100 is considered the highest acceptable level. </p>
<p>No formal pollution alert was declared, but the levels were enough to earn a rare “extremely bad” rating from the city’s air-quality monitoring network. </p>
<p>Alerts, which can force some vehicles to stay off the road, are normally declared when pollution reaches between 1.5 and 2 times acceptable limits.</p>
<p>PM10 particles are often from dust or soil kicked into the air, and the network warned that high winds were likely to cause an increase in particle levels.</p>
<p>Ozone and extremely small particles, known as PM2.5, are often triggered by vehicle emissions and are traditionally more of a problem in Mexico City. But they did not appear to play as much of a role in Sunday’s pollution spike.</p>
<p>Spring is dry season in central Mexico and it is also a time when farmers on Mexico City’s outskirts traditionally burn grass and weeds to prepare fields for planting. </p>